This invention generally relates to orthotic devices for controlling instabilities in joints, and is specifically concerned with an improved knee orthosis for providing four-point fixation against medial-lateral, anterior-posterior, and rotary knee instabilities through a mechanism that is relatively lightweight and non-bulky.
Orthotic devices for correcting knee instabilities are known in the prior art. These devices are often comprised of a mechanical joint and a pair of bracing members. The mechanical joint includes a pair of sidebars, each of which has a pivoting joint in its middle portion. The top and bottom ends of the sidebars are connected to the bracing members. The bracing members circumscribe the regions of the leg above and below the kneejoint, and support the pivoting joints of the sidebars in alignment with the kneejoint. Such prior art devices generally operate by confining the movement of the kneejoint as it bends so that unwanted motions of the lower femur and the upper tibia are eliminated or at least minimized.
Knee instabilities can take a variety of forms, including varus, valgus, rotary, anterior and posterior displacements, as well as hyperextension of the joint. Varus-type instabilities tend to bend the kneejoint outwardly, giving the leg a bow-legged orientation, while valgus instabilities tend to bend the joint inwardly, giving the leg a knock-kneed appearance. Rotary instabilities can cause femural and tibial sections of the knee to rotate excessively with respect to one another as the knee flexes. Anterior instabilities tend to separate the tibia anteriorly with respect to the femur while hyperextension-type instabilities allow the kneejoint to bend more than 180.degree. with respect to one another.
A properly installed orthotic knee brace can counteract all of these instabilities (at least in part) by reinforcing the kneejoint as a whole, and by supporting it against such unstable movements when the kneejoint flexes. Such devices are often needed by athletes in the running sports, such as, for example, football, hockey and tennis, who have suffered injuries to their joints which make them much more prone to such unstable movements. For athletic applications, such orthotic devices should be capable of eliminating or at least minimizing all such unstable movements without impeding the proper movement of the knee in any way. Moreover, such a device should be lightweight and non-bulky so that it will neither detract from the athletic performance of the athlete by either weighing the athlete down or by rubbing against his other leg during a competitive sport. It would, of course, be desirable for the orthosis to be enclosable within a uniform. Finally, such an orthosis should provide "four-point fixation" against anterior and posterior displacements as well as varus and valgus deviations. In this context, four-point fixation means that the orthosis will resist, in at least two separate points in its structure, any shear force applied across its longitudinal axis either in the plane that the kneejoint bends (in order to prevent anterior and posterior displacements), or in the plane orthogonal thereto (in order to prevent varus-valgus instabilities). Such four-point fixation is particularly important for athletes whose kneejoints have been injured to the extent where a large amount of extra support is absolutely necessary.
While knee orthoses are known which are capable of providing four-point fixation, the mechanisms which these orthoses employ are all relatively heavy and bulky, and hence capable of impeding the performance of an athlete in a running sport. While it is possible to reduce both the size and weight of the structure used in such an orthosis, such "stripping down" of the parts of the orthosis reduces its structural strength, and hence renders it less effective in providing support against knee instabilities.
Clearly, what is needed is a knee orthosis which is capable of firmly providing four-point fixation against all knee instabilities, in a structure having less weight and less bulk than prior art knee orthoses. Ideally, such an orthosis should be simple in structure, and compact enough to be easily covered by an athletic uniform.